1. Field of the Invention
The present invention relates to a speckle interference apparatus. More particularly, the invention relates to a speckle interference apparatus having means for drawing phase information to enable the phase information of speckle interference fringe patterns (speckle patterns) to be detected with a high precision, for example.
2. Related Background Art
There have hitherto been proposed various measuring apparatuses in which the coherent light emitted from a light source is irradiated onto the light diffusion surface of an object to be measured, and the interference fringes thus obtained from the measurement object, the so-called speckle interference fringes, are utilized for the purpose. These measuring apparatuses have a wide range of applications because non-contact measurements can be conducted without selecting measuring planes.
In this respect, the way to draw the required information form the speckle interference fringes which are fundamentally regarded as noise is an important factor to be considered for speckle pattern application measurements.
In conventional measuring apparatuses utilizing the speckle patterns, spectral analyses are carried out on the shifting amounts and changes of sizes of speckle interference fringes in accordance with the frequency signals obtained from light receiving elements to read the shifting amount by integrating the frequency shifts proportional to the traveling velocity of the object to be measured. Also, as these light receiving elements, CCDs are employed in many cases and, therefore, image processing is required to process the signals thus obtained.
Here, although there is a feature for the various measurements utilizing speckle interferometers that measurements can be performed regardless of the condition of the measuring surface(s), it is difficult to effectively generate measurable interference fringes for diverse measuring planes unless the reflective amount of light from the reference surface is adjusted in response to the reflectivity of the respective measuring surfaces.
Conventionally, a measuring apparatus using speckle interferometers uses a reference surface having substantially the same reflectivity as the measuring surface in order to enhance the speckle interference fringes to the extent that its contrast can be processed or inserts an ND filter into the portion where the reflectivity is higher to balance the amounts of light.
In the conventional speckle interference apparatus, however, there is a problem that the light receiving elements and the signal processing method are complicated when the image processing is executed. Furthermore, there has been a problem that it is difficult to conduct high-speed data processing due to the signal processes required for the CCD, image processing, and others.
Further, there has been a problem with the allowable speed of the measurable traveling and changes of an object being limited by the speed with which the image processing and other signal processes are executed.
Further, for the method which utilizes the nature of the speckle itself, the measuring surface should be throughly rough, and if it is a mirror or glossy surface, the intended measurement becomes difficult.
And further, the method using the ND filter when the reflective amounts of light from the measuring surface and reference surface should be adjusted, has caused a problem that the reference surfaces and ND filters must be replaced each time the measuring plane is changed. Nor is it possible to adjust the balance of the amounts of light continuously, which presents a great difficulty in enhancing the contrast of the interference fringes effectively.